AoC 2021 Day 1

Setup

Mix.install([
  :kino,
  {:nx, github: "elixir-nx/nx", sparse: "nx"}
])

input = Kino.Input.textarea("Puzzle Input")

Part 1

input
|> Kino.Input.read()
|> String.split("\n", trim: true)
|> Enum.map(&String.to_integer/1)
|> Enum.chunk_every(2, 1, :discard)
|> Enum.count(fn [left, right] -> right > left end)

Part 2

input
|> Kino.Input.read()
|> String.split("\n", trim: true)
|> Enum.map(&String.to_integer/1)
|> Enum.chunk_every(3, 1, :discard)
|> Enum.chunk_every(2, 1, :discard)
|> Enum.count(fn [[left, m1, m2], [m1, m2, right]] -> right > left end)

Part 1 - Nx

tensor =
  input
  |> Kino.Input.read()
  |> String.split("\n", trim: true)
  |> Enum.map(&String.to_integer/1)
  |> Nx.tensor()

Nx.greater(tensor[1..-1//1], tensor[0..-2//1])
|> Nx.sum()
|> Nx.to_number()

Part 2 - Nx

input
|> Kino.Input.read()
|> String.split("\n", trim: true)
|> Enum.map(&String.to_integer/1)
|> Nx.tensor()
|> Nx.window_sum({3})
|> then(fn tensor ->
  Nx.greater(tensor[1..-1//1], tensor[0..-2//1])
end)
|> Nx.sum()
|> Nx.to_number()

Part 1 - Recursion

defmodule Recursion do
  def recur([left, right | tail], acc) when right > left, do: recur([right | tail], acc + 1)
  def recur([_left, right | tail], acc), do: recur([right | tail], acc)
  def recur([_], acc), do: acc
end

input
|> Kino.Input.read()
|> String.split("\n", trim: true)
|> Enum.map(&String.to_integer/1)
|> Recursion.recur(0)

Part 2 - Recursion

defmodule Recursion do
  def recur([left, m1, m2, right | tail], acc) when right > left,
    do: recur([m1, m2, right | tail], acc + 1)

  def recur([_left, m1, m2, right | tail], acc), do: recur([m1, m2, right | tail], acc)
  def recur([_, _, _], acc), do: acc
end

input
|> Kino.Input.read()
|> String.split("\n", trim: true)
|> Enum.map(&String.to_integer/1)
|> Recursion.recur(0)